Field of the Invention--The present invention relates generally to an electromechanical system for infusing analgesia or like medication into a patient on demand by the patient, and more particularly to an attachment for use with a main pump unit containing a prime mover and a control system for controlling the operation of a disposable cassette containing a fluid pump which is mounted on the main pump unit, the attachment including both a compartment for securely storing the medication supply and means for preventing either the cassette or the fluid line between the storage compartment and the cassette removed or tampered with.
One of the longest-standing objectives of medicine has always been the efficacious alleviation of chronic and incessant pain. It has often been difficult to effectively control such severe pain even though a number of highly effective painkilling medications are widely known. Since it is difficult for a physician to objectively measure pain in a patient, it has remained difficult to accurately control pain in a manner affording consistently helpful relief to the patient.
Dosage of painkilling medication is based on general dosage guidelines which minimize dosage to prevent side effects of the drug. Such general guidelines often provide inadequate assistance since the effects of any particular medication may vary widely between patients. Accordingly, pain is often either overcontrolled or undercontrolled in many patients, with the corresponding side effects of either a sedative effect or an inadequate diminution in the level of pain, respectively.
In the past there have been two primary techniques which have been used to deliver drugs to a patient- oral ingestion and intramuscular injection. The first technique is accomplished by having the patient swallow pills or a liquid. The second such technique is through an intramuscular injection, or shot, using a syringe and needle which, like oral administration, delivers a large dosage at relatively infrequent intervals to the patient. These techniques are generally unsatisfactory, particularly when the drug being administered is a painkiller which is potentially lethal, has negative side effects when delivered in a large dosage, or must be delivered more or less continuously to achieve the desired therapeutic effect.
In the administration of painkilling medication by either oral ingestion or by intramuscular injection, a sufficient amount of the medication is administered to last at least several hours. This typically initially overmedicates the patient, with a steady diminution in effect representing increasing pain until another injection is administered and takes effect. This problem may result in smaller doses or injections being given at more frequent intervals, a compromise approach not yielding wholly satisfactory results.
As an alternative to these two techniques of administering medication to a patient, the relatively recent addition of patient-controlled analgesia (PCA) pumps has come as a welcome improvement. PCA pumps may be utilized to administer painkilling drugs intravenously to a patient in smaller, metered doses at frequent intervals on demand by the patient, within limits prescribed by a physician. Since the medication is administered directly into the bloodstream, relief is virtually immediate. PCA pump therapy may be electronically controlled to deliver precise, metered doses immediately upon demand by the patient, thereby providing a beneficial administration of painkilling medication to the patient whenever it is needed.
Since the overmedication associated with intramuscular or oral delivery is avoided, in some patients significantly less painkilling medication is required with PCA pump therapy than with conventional therapies. PCA pumps are particularly effective in treating terminally ill patients, and have been used effectively for intraspinal and subcutaneous infusions. Recent advances in equipment have allowed the PCA pump to be used in a home care setting in addition to its use in a hospital setting.
A multi-purpose infusion system capable of operating as a PCA pump is disclosed in U.S. patent application Ser. No. 127,333, now U.S. Pat. No. 4,832,299 entitled "Disposable Cassette for a Medication Infusion System," and assigned to the assignee of the present application, which application is hereby incorporated herein by reference. In this system, a disposable cassette contains a piston-type fluid pump and active valves to pump fluid, with the piston and valves in the cassette being operated by a mechanical drive system located in and controlled by a main pump unit. The cassette includes a slide latch for latching the cassette in place on the main pump unit, which slide latch also closes the fluid path before the cassette is installed and when it is removed, the slide latch only being opened when the cassette is properly installed on the main pump unit.
The cassette has an inlet tube designed to be connected to a fluid reservoir or other fluid source, and a fluid outlet tube designed to be connected to an administration set for delivery to a patient. The main pump unit has one of its three channels which may be configured as a PCA pump, and an input to the main pump unit may be used as the channel to actuate the pump at the patient's request. Administration is controlled by specifying demand dose volume (bolus volume), lockout interval (the minimum time between administration of doses, also called the refractory period), and maximum dosage over a given time period (four hours, for example). Additional commands which may optionally be utilized are a loading bolus (administered at the beginning of PCA therapy to quickly increase serum concentration of the drug) and continuous infusion (a basal rate to maintain an appropriate serum level, thereby minimizing the number of demand doses).
The system may be used to administer narcotic drugs such as morphine, meperidine, and fentanyl. It will of course be realized by those skilled in the art that such drugs are controlled substances, normally kept under lock and key. As such, the use of these drugs in a PCA pump requires a substantial amount of the drug to be located in a reservoir accessible by the PCA pump. It is therefore necessary to provide a sufficient level of security to prevent theft of the drug.
A device used to secure the infusion system described above to an IV pole is disclosed in U.S. patent application Ser. No. 128,744, now U.S. Pat. No. 4,872,813 entitled "Clamp Fixture," and assigned to the assignee of the present application, which application is hereby incorporated herein by reference. However this clamp is designed only to secure the main pump unit to the IV pole, and does not secure the medication being pumped by the system.
It is therefore the primary object of the present invention to provide a mechanism for securing the supply of medication in the reservoir located near the PCA pump. In order to accomplish this purpose, the reservoir itself must first be secured to prevent it from being stolen or removed from the location of the PCA pump. Since the PCA main pump unit discussed above is secured to an IV post, it is an objective of the present invention to secure the medication to the main pump unit to prevent its theft or removal.
In order to make not just the medication reservoir but the entire fluid system secure, it is also vital to protect the fluid line between the medication reservoir and the cassette. The present invention must also accomplish this end, since if the fluid line is left unprotected, it would be simple for an unauthorized individual to open the fluid line between the medication reservoir and the cassette and drain the medication reservoir. Accordingly, it is an objective of the present invention to protect the integrity of the fluid line between the medication reservoir and the cassette.
The design of the cassette allows the system to be primed when the cassette is removed from the main pump unit. The priming operation allows medication to flow freely through the cassette, a situation which would be potentially deadly were it to occur with an administration set delivering medication from the cassette to the patient. Accordingly, it is a further objective of the present invention that it prevent the unauthorized removal of the cassette from the main pump unit.
The security provisions which are objectives of the present invention should all operate to prevent both any action by a patient or any tampering by an unauthorized individual from violating the security of the medication being administered. The security attachment of the present invention must be relatively compact in size, yet be capable of holding the several different sizes and configurations of medication containers. Specifically, the device must be capable of containing various size syringes, as well as small flexible plastic medicine bags. In addition, the device must be relatively inexpensive of construction, to thereby afford it the most advantageous market advantage. Finally, the system of the present invention must accomplish all of the aforesaid objectives and advantages without incurring any relative disadvantage.